Displacing magnetic charges or hard magnets mechanically generates varying electromagnetic fields, which can provide a means for transmitting very low frequency (VLF) electromagnetic waves. VLF electromagnetic waves have a frequency from 3 to 30 kHz, which corresponds to wavelengths from 100 km to 10 km. VLF electromagnetic radiation has found use in long distance communication, for example communication with submarines. Mechanically displacing hard magnets for radiating electromagnetic waves presents several challenges, such as extremely low radiation efficiency due to energy losses resulting from large frictional forces. In particular, achieving a high linear or angular velocity at 10 kHz or above is challenging due to the limited angular speed achieved by mechanical motors.
Typically, an antenna receives information in the form of electromagnetic waves, whereby electrons in the antenna are pushed by the electric field, leading to the production of oscillating voltage and current. To receive and transmit an electromagnetic wave, the length of the antenna has to roughly match a fraction of the wavelength of the electromagnetic wave (e.g., ½ or ¼th of the wavelength). The common half-wave dipole antenna consists of two quarter-wavelength antenna elements arranged end to end, each connected to a transmission line. Because of the dependence of the antenna size on wavelength, a full size antenna capable of transmitting VLF waves (3 kHz to 30 kHz) would need to be very large. In general, however, the length of a VLF transmitting antenna is only a small fraction of the length of the VLF wave. Such an antenna radiates only a fraction of the transmitter power. Also, long distance communication requires the use of high power transmitters.
There is a need for compact, mobile, and power efficient VLF magnetoelectric antennas for use in communication systems.